This section is intended to provide a background or context to the invention that is recited in the claims. The description herein may include concepts that could be pursued, but are not necessarily ones that have been previously conceived or pursued. Therefore, unless otherwise indicated herein, what is described in this section is not prior art to the description and claims in this application and is not admitted to be prior art by inclusion in this section.
Motion Compensated Prediction (MCP) is a technique used by many video compression standards to reduce temporal redundancy present in a video sequence. Temporal redundancy refers to those situations where objects, for example, appearing in one frame of the video sequence are likely to appear in subsequent frames. In MCP, a prediction for the current frame is formed using previously coded frame(s) and only the difference between the original and the prediction signal is encoded and sent to the decoder. The prediction signal, representative of a prediction frame, is formed by first dividing the frame into blocks, e.g. macroblocks, and searching a best match in the reference frame for each block. In this way, the motion of the block relative to reference frame is determined and this motion information is coded into the bitstream as motion vectors (MV). A decoder is able to reconstruct the exact prediction by decoding the motion vector data embedded in the bitstream.
The motion vectors do not necessarily have full-pixel accuracy but could have fractional pixel accuracy as well. This means that, motion vectors can point to fractional pixel locations of the reference image, or frame, where the fractional pixel locations can refer to, for example, locations “in between” image pixels. In order to obtain the samples at fractional pixel locations, interpolation filters are used in the MCP process. Conventional video coding standards describe how the decoder should obtain the samples at fractional pixel accuracy by defining an interpolation filter. In MPEG-2, for example, motion vectors can have at most half pixel accuracy and the samples at half pixel locations are obtained by averaging the neighboring samples at full-pixel locations. The H.264/AVC video coding standard supports motion vectors with up to quarter pixel accuracy where half pixel samples are obtained by symmetric-separable 6-tap filter and quarter pixel samples are obtained by averaging the nearest half or full pixel samples.
In order to improve the prediction performance in video coding, it is generally desirable to adapt interpolation filter coefficient values according to local properties of the image. These filters are referred to as adaptive interpolation filters (AIF). Certain methods and systems have been developed to provide interpolation filters with adaptive filter coefficient values to manage, for example, aliasing in an image acquisition process, such as those described in “Coding of Coefficients of two-dimensional non-separable Adaptive Wiener Interpolation Filter”, Proc. VCIP 2005, SPIE Visual Communication & Image Processing, Beijing, China, July 2005, and in U.S. Patent Publication No. 2004/0161035 to Wedi, entitled “Device for Interpolating of Scanning Values and Image Encoder and Decoder,” all of which are incorporated herein by reference in their entireties. International Patent Publication No. WO 03/058945, entitled “Coding Dynamic Filters,” to Lainema, incorporated herein by reference in its entirety, describes coding filter coefficient with respect to a base-filter and adapting the base-filter according to statistics gleaned from a video sequence.
It would be desirable to further increase error resiliency in conjunction with the coding of filter coefficients and to keep the coding efficiency high.